1. Technical Field of the Invention
The present invention relates to mobile telecommunications systems and, in particular, to the validation of a forward-to-number for call forwarding subscriber features in a mobile telecommunications network.
2. Description of Related Art
In a typical mobile or wireline telecommunications system, a subscriber activates his call forwarding features by first establishing a speech connection with the telecommunications network serving the subscriber and then by manually inputting a desired forward-to-number. For example, the subscriber dials service code *76 for the Call Forwarding Don't Answer (CFDA) feature followed by a specific forward-to-number to activate the CFDA feature. Even though the subscriber might already know the validity of the forward-to-number, it is prudent to physically establish a speech connection with the entered forward-to-number to confirm that all future calls will indeed be forwarded to the correct number and that desired parties will be available to answer the forwarded calls. Accordingly, after receiving the entered forward-to-number, the telecommunications network initiates an outgoing call toward the forward-to-number to physically establish a speech connection between the subscriber and the telephone terminal associated with that particular forward-to-number (this action will hereinafter be referred to as the validation call). By means of the validation call, the system ensures that the forward-to-number is a valid and correct directory number within the telecommunications network. If the subscriber has inadvertently dialed a wrong number, or an unwanted user has answered the validation call, the subscriber is alerted and can abort the activation process. If the mobile subscriber confirms the validation call, all unanswered incoming calls to the mobile station are subsequently forwarded to the forward-to-number.
In the Global System for Mobile (GSM) or Personal Communications System (PCS) environment, a speech connection with the serving mobile switching center (MSC) is not utilized to activate or deactivate special subscriber features. With the development of data channels or control channels separate from the voice channel, mobile stations can communicate data with a Public Land Mobile Network (PLMN) without utilizing a speech connection. As an illustration, within the PCS environment, a mobile station displays a menu enumerating the available options to a mobile subscriber. The mobile subscriber selects the desired feature option, such as the activation of the CFDA feature, and enters the subsequently needed forward-to-number. A Direct Transfer Application Protocol (DTAP) based message, such as a Radio Interface Layer 3--Call Control (RILC3-CC) message, encapsulating the activation request along with the forward-to-number is transported to the serving PLMN over a connection-less communications link such as a Fast Associated Control Channel (FACCH) or Stand-alone Dedicated Control Channel (SDCCH). The serving Mobile Switching Center (MSC) receives the DTAP based message, extracts the encapsulated activation request and the forward-to-number, and alters the state of the CFDA feature to reroute all future incoming calls intended for that particular mobile station to the designated forward-to-number.
However, because there is no speech connection between a mobile station and the serving MSC, and the data channel is incapable of transporting voice data, the mobile telecommunications network is unable to provide verbal verification between the mobile station requesting the activation of a call forwarding feature and the telephone terminal associated with the specified forward-to-number. There is accordingly a need for a method and apparatus to validate an activated forward-to-number associated with a call forwarding feature within the PCS or GSM environment.